(1) Field of the Invention
The invention relates to a method and a device for individual grain sorting of objects from bulk materials, in particular broken mineral ores, crushed and whole plastics from waste materials, comminuted wood on a conveying device having an actuable discharge unit which separates into fractions the bulk material identified according to type.
(2) Description of Related Art
Such methods and sorting devices are known in process engineering.
In addition to systems in which the material to be sorted is X-rayed and is then sorted using the composition of the emitted radiation as a sorting criterion, systems are also known which use the intensity and spectral composition of visible light as so-called colour sorting.
Thus, in accordance with EP 0 737 112 B1/DE 694 30 386 T2, by means of                a conveying device with a uniformly contrasting background for the particles to be conveyed and sorted, and a controlled light mounted above it,        a position sensor for determining the position of the particles with a logic for sub-dividing a viewing area into a matrix of cells with a number of pixels with a first controller,        an image detector for acquiring a colour image,        an image processor for receiving data from the viewing area and        a separating device activated by a second controller,scrap particles are sorted by their colour on the basis of difference signals.        
This system is based on the proven technological process of sensor-driven sorting techniques, such as data acquisition—data computation—sorting decision—control of a conveying device. This solution is suitable for sorting scrap materials if the colour is used as a sorting criterion. If the material colour that can be used as a sorting criterion is covered by a layer of dirt or materials, then these systems are not applicable.
In the source document “http://www.besttoratec.com/sorter/Helius_laser-sorter.htm” a line laser has already been described as a lighting means, however not for a 3D-recognition process, but as an emitter for a colour camera.
In addition, page 3 of the source “http://www.sick.fi/ch/products/machinevision/ruler/de.too lboxpar.0008.file.tmp/ProduktinformationRuler.pdf” discloses the use of a laser line width as “scattered laser light” for sorting purposes.
According to this article, in classification applications in the timber industry both form and surface properties of objects are to be evaluated. In addition to the measurement of the object outline a grey-scale image and an image with the surface information can be generated at the same time (scattered laser light effect or tracheid effect). In the timber classification example the shape of the timber product, which can be geometrically identified in advance, is measured, which means only errors such as knots and resin pockets can be detected. With this information the timber items are then sorted according to the aforementioned quality features—not in accordance with indeterminable shapes.
While in such applications it is true that the timber is subject to high-speed measurement, but not according to a sorting criterion based on the detection of indeterminably occurring shapes of the sorted object.
Furthermore, from US 2010 0 290 032 A1 in order to sort plastic, fabric, foodstuffs, paper, glass, metal, it is known to use a steered laser in the infrared spectrum by means of a rotating mirror wheel, but which cannot continuously take a measurement at all positions, because the information is sent sequentially through the mirror to the local point sensor. This solution only permits detection based on a spectral composition.
A review of U.S. Pat. No. 6,914,678 B1 discloses lamps emitting IR or visible light for the automatic detection and sorting of types of plastic, in particular, in waste products. A mirror is used to deflect the IR or visible light and a camera as a detection unit. Although several wavelengths can be detected at the same time, it is only possible however to construct a non-IR spectrum or the visible spectrum of the reflected light, and only spectral differences are detected.
In another subject area, namely the detection of differences in the tissue of living organisms such as humans or animals, according to WO 2006/038 876 A1 non-visible lasers such as “monolithic lasers” with rapidly varying wavelength are used as a system for generating O (optical) C (coherence) T (tomography) images by the method of interferometry. This system is used for the detection of intervals by modulating the wavelength. It can also be applied in materials inspection, for the detection of cracks or irregularities in the material. By using a modulatable point laser with deflecting mirrors only the internal structure can be detected, but not the surface.